Den 05-05-2011 16:48, Marsh Ray skrev:
On 05/05/2011 05:52 AM, Thorsten Ottosen wrote:
T* has the distict advantage that it is optimally efficient, even though that optional<T&> might slightly be more type-safe.
sizeof(T*) is guaranteed to be nonzero, and in practice is 4 or 8 bytes, whereas references are allowed to have no size at all.
Can you mention just one ABI where references are merely pointers?
References have a very restricted set of allowed behaviors. Pointers are first-class values in their own right and this makes it impossible (in the general case) for a compiler to know if an object is being aliased by other pointers. You make the optimizer's job much, much harder by taking the address of something. It depends on a lot of factors of course, but there are cases where references are faster than pointers, so T* is not necessarily "optimally efficient".
perhaps, but in this case the reference /is/ a dereferenced pointer from within a map. -Thorsten